I agree that moving in is a major step in any relationship, and with poly relationships, everything is that much more complicated ('cause there's more people involved). I know that the three of us have really only cleared the first hurtle in our joint relationship together, but that first hurtle was a doozie... it told us if we could even handle forming a poly family in the first place.
In order to accept being a poly family, I had to explore and be completely comfortable with all of my options, including divorce and remariage. I had to explore my feelings of jealousy and compersion. I had to experience first hand how it would feel to share my wife's time with someone else. And I had to re-think all of my values regarding relationships and sexuality, with a completely open mind and willingness to accept the outcome, whatever is it. It was a difficult process and challenged the very bedrock of my belief system (being a staunch mono and all). There were periods of time where I had no moral compass or role models to guide me through it, other than the unconditional love I have for my wife. In Christian circles, we refer to this as "agape love" (http://www.gotquestions.org/agape-love.html
). I also prayed to God for guidance.
(Did I mention before that I'm a romantic and a Christian. Damn... I'm just about as vanilla as they come! LOL)
From day #1, I've always felt compersion for my wife in recognizing she is bi and finding/falling in love with her wife. (I'm no longer going to refer to my wife's wife as an "OSO" because that implies a letter position in the vee. As far as I'm concerned, we're both my wife's primaries.) I saw the positive effect that all this all had on my wife, and something that wonderful can't be all bad. ;-) Furthermore, I like my wife's wife too... not in a romantic way but as a friend. She's a great person, and we all get along wonderfully. I'm sure that helps a lot in making a vee work.
One by one, I overcame my various concerns and jealousies while reforging and redefining my relationship with my wife, until there was really just one remaining issue... could I handle sharing my wife's time with someone else? I didn't think I could; I thought that may ultimately be the deal-breaker in all this, and I was mentally prepared to handle the consequences. But by having my wife's wife stay with us, we were able to resolve this last major issue / fear and figure out how to make it work for everyone. It was an eye opener, and it was the last major fear or hangup I had. I now just left with compersion for this new relationship, and I see it as wonderful. I still have jealousies from time to time, but they're more "cute" than hurtful.
Bottom line: I look forward to having my wife's wife move in is because it moves our relationship forward in a positive way. That's not to say we won't have challenges... everyone does, even mono couples after almost 20 years of marriage. But we'll all be together to resolve them, together, and become stronger in the process. And if ultimately this relationship is not meant to be (which I doubt), then that will become apparent as well and we'll address that too. Either way, moving-in is our next logical step, and we're (naively perhaps) plowing forward! Yea! ;-)
One funny side effect (that I didn't expect) of all this exploration is that I feel a step closer to being poly myself. I love the idea of adding one more to our family over time and adding a couple more kids. I don't know if we'll ever do this for reals... it's more of a long-term vision than anything we want to do right now. For the time being, I'm focused on continuing to rebuild the relationship with my wife. We have a lot of fun dating planned, catching up for lost time! ;-)